ECM Input EI72: Throttle Switch Circuit: Notes

The throttle switch is part of the ISC. Pin "B" of 4-way Weatherpack connector on ISC is throttle switch or closed throttle input to ECM. The ISC throttle switch contacts are normally open and closed when throttle linkage contacts ISC plunger (closed throttle, ISC in control of idle speed).

The ECM sends a 5-volt signal to pin "B" of ISC motor on circuit No. 427. When throttle linkage resets on ISC plunger, the throttle switch contacts close, shorting ISC, pin "B" to pin "A" on ground circuit No. 450. The 5-volt signal from ECM is grounded at closed throttle, resulting in zero volts at ECM pin "D15". When throttle is opened, the throttle switch opens pin "B" on circuit No. 427, resulting in 5 volts at ECM pin "A7".

On the diagnostic display, "HI" is an open switch (open throttle), while "LO" is a closed switch (closed throttle).